The present invention generally relates to recording and reproducing systems for recording and reproducing signals on and from a first system rotary recording medium so that the first system rotary recording medium is compatibly playable on a reproducing apparatus which is primarily designed to play a second system rotary recording medium. A rotary recording medium has first kind of track turns which are recorded with analog signals mainly comprising a composite video signal of a first television system which employs 625 scanning lines and a field frequency of 50 Hz or a composite video signal of a second television system which employs 525 scanning lines and a field frequency of 59.94 Hz, and a second kind of track turns which are recorded with digital signals made up of audio information and/or still picture information, and the first and second kinds of track turns coexist on the same surface of the rotary recording medium. More particularly, the present invention relates to a recording and reproducing system for recording and reproducing such signals on the rotary recording medium so that the rotary recording medium is compatibly playable on a reproducing apparatus of a television system employing a horizontal synchronizing signal frequency which is different from the horizontal synchronizing signal frequency of the recorded signals on the rotary recording medium which is being played.
There is a known type of a rotary recording medium (hereinafter simply referred to as a disc) which is recorded with analog information signals such as a composite video signal and audio signals. In such a disc, the analog information signals are subjected to a frequency modulation, for example, and are recorded on a spiral track or concentric tracks on the disc as variations in geometrical configuration, for example. This disc is often referred to as a video disc because the recorded information mainly includes the composite video signal. The composite video signal or the like is recorded on the track turns on the video disc in the form of modulated signals which are obtained by modulating a carrier by the analog information signals. An address signal which is used for random access and the like, is recorded within a predetermined duration within a vertical blanking period of the composite video signal, for example. The address signal itself is an encoded digital signal, however, the main information recorded on the video disc is the analog modulated composite video signal or the like. Hence, in the present specification, track turns such as the recorded tracks of this video disc, will be referred to as "analog recorded track turns" for convenience' sake.
On the other hand, there is another type of a disc which is recorded with digital signals. In such a disc, audio signals or audio and video signals are subjected to a digital modulation, and are time-sequentially multiplexed and recorded on concentric tracks or a spiral track on the disc as variations in geometrical configuration, for example. This disc is often referred to as a digital audio disc because the recorded information mainly includes the audio signals, and the video signal mainly relates to a still picture and is simply recorded as a supplementary information to help the listener with his imagination. The audio signals or the audio and video signals are recorded on the track turns on the digital audio disc after being converted into the form of digital signals which are obtained by subjecting the audio signals or the audio and video signals to a digital modulation and then subjecting the digital modulated signals to a frequency modulation or the like. In the present specification, track turns such as the recorded tracks of this digital audio disc, will be referred to as "digital recorded track turns" for convenience' sake.
In an electrostatic capacitance type video disc proposed in a U.S. Pat. No. 4,331,976, the recorded signals are reproduced from the video disc by detecting the variations in the electrostatic capacitance which is formed between the video disc and an electrode of a reproducing stylus. Reference signals for tracking control, are recorded on both sides of the information signal recorded track (analog recorded track). According to this video disc, the need for a stylus guide groove was eliminated by use of the reference signals, as is known. In this known video disc, a tracking control was carried out with respect to the reproducing stylus so that the reproducing stylus accurately scans over the information recorded track during the reproduction mode, by comparing the levels of the reference signals which are reproduced from the video disc.
On the other hand, an electrostatic capacitance type digital audio disc is also known. The electrostatic capacitance type digital audio disc has no stylus guide groove and is recorded with reference signals for tracking control on both sides of the information signal recorded track (digital recorded track), similarly as in the case of the electrostatic capacitance type video disc. During the reproducing mode, this electrostatic capacitance type digital audio disc is rotated at a predetermined rotational speed which is the same as the rotational speed of the electrostatic capacitance type video disc. The frequencies of the reference signals and the method of reproducing the reference signals, are the same between the electrostatic capacitance type digital audio disc and the electrostatic capacitance type video disc. Further, in both the electrostatic capacitance type digital audio disc and the electrostatic capacitance type video disc, the recorded signals are reproduced from the disc by detecting the variations in the electrostatic capacitance between the disc and the electrode of the reproducing stylus. For these reasons, even when the digital audio disc is played on a video disc reproducing apparatus which is designed to play the video disc, the tracking control is carried out with respect to the reproducing stylus similarly as in the case where the video disc is played, and the recorded signals can be picked up and reproduced from the digital audio disc by the reproducing stylus. The signals which are reproduced from the digital audio disc, are demodulated into original audio signals or the like in an adapter which is coupled to the video disc reproducing apparatus.
Accordingly, the previously proposed electrostatic capacitance type video disc and the electrostatic capacitance type digital audio disc can be played on the same electrostatic capacitance type video disc reproducing apparatus. In other words, the above video disc and the digital audio disc can be played compatibly on the same video disc reproducing apparatus.
However, the digital audio disc and the video disc were mutually independent discs, and the compatibility did not exist in the true sense of the word. On the other hand, the digital audio disc is recorded with digital signals. Thus, compared to the video disc, the audio signals are reproduced from the digital audio disc with a wide dynamic range and with an extremely high fidelity, due to the characteristics of the digital signal transmission. Moreover, the still picture which is reproduced from the digital audio disc is extremely sharp, and there is of course an advantage in that the audio signals are reproduced from the digital audio disc with an extremely high fidelity together with the still picture. On the other hand, the still picture is reproduced from the video disc by repeatedly reproducing the same track turn on the video disc. Generally, the audio signals are muted during the still picture reproduction, and it is impossible to simultaneously reproduce the audio signals and the video signal from the video disc. However, due to the analog signal transmission in the video disc, it is possible to transmit the information signals in real time with a frequency band in the range of several MHz according to the video disc. Thus, compared to the digital audio disc in which the information signals are transmitted with a frequency band in the range of several tens of kHz in order to improve the transmitting accuracy, the video disc is advantageous in that it is possible to simultaneously reproduce a moving picture and the audio signals. Accordingly, in order to ensure optimum reproduction of the recorded signals, it is desirable to select and reproduce one of the digital signals and the analog signals depending on the information contents.
Accordingly, in a U.S. patent application Ser. No. 609,237 filed May 11, 1984 in which the assignee is the same as the assignee of the present application, a novel and useful reproducing apparatus was proposed. According to this proposed reproducing apparatus, the analog recorded track turns and the digital recorded track turns coexist on the disc depending on the recorded information content, and the recorded information signals are satisfactorily reproduced from the disc regardless of whether the the track turn being scanned is the analog recorded track turn or the digital recorded track turn. Hence, the advantages of the video disc and the digital audio disc can both be exhibited to the maximum, and the video disc and the digital audio disc are compatibly playable on the reproducing apparatus.
In addition, in this proposed reproducing apparatus, the disc which is recorded with a composite video signal of one television system on the analog recorded track turns thereof, is compatibly playable on a reproducing apparatus which is primarily designed to play a disc which is recorded with a composite video signal of a different television system, and the recorded composite video signal is reproduced as the composite video signal of the different television system. Such compatible reproduction is achieved by controlling the rotational speed of the disc so that the recorded horizontal synchronizing signal is reproduced from the disc with a frequency which is equal to a horizontal synchronizing signal frequency of the television system which is set for the reproducing apparatus, as is done in a compatibly reproducing means disclosed in a U.S. Pat. No. 4,445,143 in which the assignee is the same as the assignee of the present application. The disc on which the analog recorded track turns and the digital recorded tracks coexist, is normally played by rotating the disc at a rotational speed which is identical to the rotational speed of the video disc which is recorded with a composite video signal of a television system which is the same as the television system of the composite video signal recorded on the analog recorded track turns on the disc. Further, the digital signals recorded on the digital recorded track turns on the disc, are reproduced at a predetermined transmission frequency (that is, at a predetermined block transmission quantity per second) of 44.100 kHz or 44.056 kHz.
For example, a first system disc is recorded with a composite video signal of a first television system employing 625 scanning lines and a field frequency of 50 Hz, on the analog recorded track turns thereof, at a rate of four fields per revolution of the disc. This first system disc is recorded with 3528 (=44.100.times.10.sup.3 .times.4.div.50.0) blocks of digital signals with a transmission frequency of 44.100 kHz on the digital recorded track turns thereof. Normally, the recorded signals are reproduced from this first system disc by rotating this first system disc at a rotational speed of 750 rpm.
However, when the recorded horizontal synchronizing signal having a frequency of 15.625 kHz is to be reproduced from the first system disc, at a horizontal synchronizing signal frequency of 15.734 kHz of a second system which employs 525 scanning lines and a field frequency of 59.94 Hz, that is, when the first system disc is to be compatibly played on a reproducing apparatus which is primarily designed for a second system disc, the first system disc is rotated at a rotational speed of 755.2 rpm which is approximately 0.7% faster than the original rotational speed of 750 rpm. As a result, the recorded digital signals are also not reproduced at the original transmission frequency of 44.100 kHz, but are reproduced at a transmission frequency of 44.408 (=44.1.times.15.734.div.15.625) kHz. Similarly, when compatibly playing the second system disc on a reproducing apparatus which is primarily designed for the first system disc, the recorded digital signals are reproduced from the digital recorded track turns on the second system disc at a transmission frequency which is different from the original transmission frequency. On the other hand, the frequency of a master clock signal for a digital signal demodulating circuit which demodulates the digital signals which are reproduced from the digital recorded track turns on the disc so as to demodulate the reproduced digital signals into the original four channels of audio signals or a still picture signal, is selected to a predetermined number (for example, 140) times the transmission frequency with which the digital signals are reproduced from the digital recorded track turns on the disc.
For this reason, when compatibly playing the first (or second) system disc on the reproducing apparatus which is primarily designed to play the second (or first) system disc, it is necessary to change the frequency of the master clock signal in addition to changing the rotational speed of the disc. Therefore, there are problems in that the construction of a phase locked loop (PLL) for generating the master clock signal is complex and expensive.